過疎【かそ】
underpopulation, low population density, depopulation
疎開【そかい】
dispersal, evacuation, removal, spreading out (troops), deployment
疎通【そつう】
(mutual) understanding, communication, passing without obstruction
疎遠【そえん】
estrangement, alienation, neglecting to stay in contact
疎外【そがい】
alienation, estrangement, leaving (someone) out, casting out, cutting off, avoiding, giving the cold shoulder
空疎【くうそ】
empty (e.g. argument), insubstantial, hollow, fruitless